Field of the Invention
The invention relates to a multi-motor drive and a method for driving a printing press.
In the drive of a printing press having a plurality of motors, the motors must be synchronized so that no disruptive register fluctuations occur in the printed image. Register fluctuations are produced due to rotational oscillations in the cylinders used for printing and due to tooth-flank changes in the gear train of the drive. Rotational oscillations at a frequency that is not an integer multiple of the printing cycle are produced, for example, when more gripper bars than one gripper bar are installed on a cylinder for conveying sheets or when reciprocable inking rollers are installed. Flank changes in a gear train occur when the torque flow direction changes in at least one gear. Flank changes occur randomly and are not predictable.
In the case of presses with a large number of printing units, it has become known heretofore, for example, from German Published, Non-prosecuted Patent Application DE 195 12 865 A1, to divide a printing press into partial presses, each partial press having its own drive motor assigned thereto. For sheet-fed rotary printing presses convertible for operation between single side and first form and perfecter printing, the division or separation location may be upstream of a reversing or turning drum of a perfecting device. The division into partial presses results in drive groups with high mechanical eigenfrequencies, i.e., natural or characteristic frequencies, due to which disruptive oscillations may be reduced if the drive gears and cylinders are positioned precisely on both sides of a separation or division location.
In the case wherein exactly one motor per partial press is installed, a partial press behaves in a manner similar to that of a single driven printing press. The rotational oscillations within a partial press cannot be compensated for satisfactorily. Due to the high mass moments of inertia of the partial presses, the synchronization at the locations of separation or division is also impaired.
German published, Non-prosecuted Patent Application DE 195 25 593 A1, corresponding to U.S. Pat. No. 5,720,222, discloses a multi-motor drive for a printing press wherein a under or a printing unit has two drive motors, respectively, assigned thereto, the printing units being decoupled mechanically from one another. With a first one of the drive motors, a basic torque is infed, while the second drive motor is a highly dynamic drive, with which the remainder of the torque, implementing the synchronism of the cylinders or printing units, is infed. A printing press having ten printing units thus has twenty drive motors, the synchronization of which is consequently quite problematical.
In a device for driving printing presses with a plurality of motors arranged decoupled, as is disclosed in German Published, Non-prosecuted Patent Application DE 197 42 461 A1, corresponding to U.S. Pat. No. 6,095,043, a transfer station with a separately controllable drive is provided between two mechanically decoupled printing unit groups. A phase offset between the printing unit groups can be compensated for by controlling the transfer station. The transfer station constitutes only a low mass, which can be managed well by appropriate control technology.
It is accordingly an object of the invention to provide a drive and a method for driving a printing press which, with little expenditure of material and low cost, rapidly and accurately permits production and maintenance of synchronism between printing unit groups.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a multi-motor drive for a printing press having a plurality of printing unit groups, comprising at least one motor provided for each of the printing unit groups, and gear trains via which the printing unit groups are synchronously driven, the gear trains, during a printing operation, being mechanically separated from one another, the at least one motor being assigned to a respective separation location between the printing unit groups.
In accordance with another feature of the invention, in addition to a main motor feeding into a respective gear train of a printing unit group, two auxiliary motors are provided for the respective separation location.
In accordance with a further feature of the invention, in addition to a main motor feeding into a respective gear train of a printing unit group, one auxiliary motor only is provided for the respective separation location.
In accordance with an added feature of the invention, in addition to a main motor feeding into a respective gear train of a printing unit group, an auxiliary motor is provided, in the case of a printing unit group located between two other printing unit groups, the auxiliary motor being assigned to a separation location.
In accordance with an additional feature of the invention, the auxiliary motors have a lower power than the main motors.
In accordance with another aspect of the invention, there is provided a method for driving a printing press, which comprises, for printing with a plurality of motors, at separation locations between gear trains mechanically decoupled from one another, infeeding torques, respectively, into the gear trains.
In accordance with a further mode, the method of the invention further comprises providing at least one main motor and at least one auxiliary motor for driving at least one gear train.
In accordance with an added mode, the method of the invention additionally comprises having the main motor serve for infeeding a torque that drives, on average, and having the auxiliary motor serve for producing a torque that brakes, on average.
In accordance with an additional mode, the method of the invention further comprises applying a constant nominal current value to the auxiliary motor.
In accordance with yet another mode, the method of the invention further comprises controlling the main motor and the auxiliary motor with respect to the rotational angle thereof.
In accordance with yet a further mode, the method of the invention further comprises setting an angular offset between the main motor and the auxiliary motor.
In accordance with yet an added mode, the method of the invention further comprises setting a constant angular offset between the main motor and the auxiliary motor.
In accordance with yet an additional mode, the method of the invention further comprises variably setting by a control system a differential angle between the main motor and the auxiliary motor, so that respective average actual current values of the auxiliary motors maintain a nominal value.
In accordance with still another mode, the method of the invention comprises providing, in a press with a plurality of separation locations, differential angles of nominal values of a closed-loop control of motors from at least one group thereof selected from a group consisting of auxiliary motors and a group consisting of main motors on both sides of the separation location which, relative to a reference press angle, are respectively constant, and determining the differential angle of the nominal value of the closed-loop control of a respective motor at a separation location of a printing unit group by an adjacent printing unit group.
In accordance with still a further mode, the method of the invention comprises providing, in a press with a plurality of separation locations, differential angles of nominal values of a closed-loop control of motors from at least one group thereof selected from a group consisting of auxiliary motors and a group consisting of main motors on both sides of the separation location which, relative to a reference press angle, are respectively constant and close to zero, and determining the differential angle of the nominal value of the closed-loop control of a respective motor at a separation location of a printing unit group by an adjacent printing unit group.
In accordance with a concomitant mode, the method of the invention further comprises performing an interference variable control when driving motors from at least one group of motors respectively selected from a group consisting of main motors and a group consisting of auxiliary motors.
Due to the provision of motors in the drive train of a printing unit group, additional possibilities of intervention result directly at a separation location, in order to prevent flank changes from occurring and to improve the synchronism under controlled operation.
A sheet-fed printing press having a relatively large number of printing units can advantageously be divided into two or more printing unit groups, which are driven mechanically decoupled from one another. A printing unit group includes a partial gear train for driving at least one paper-carrying element, such as a cylinder. Each partial gear train can be driven by a main motor and by one or two auxiliary motors. The number of auxiliary motors depends upon the number of adjacent printing unit groups. The auxiliary motors infeed the torque thereof, respectively, at a separation location between the printing unit groups. It is possible to provide an auxiliary motor for each separation location. The auxiliary motors are acted upon with a constant torque or operated under control, coupled to a measuring device. The main motors continuously introduce a driving torque into the respective partial gear train and are controlled with the aid of the feedback of a measured variable, which is determined by a measuring sensor. Examples of the measured variables are the angular position, the speed and/or the acceleration directly at the motor shaft or at any desired shaft in the respective printing unit group. At all times, the auxiliary motors introduce a braking torque into the printing unit groups.
The auxiliary motors can be operated in different ways. In one possible embodiment, the auxiliary motor is acted upon by a constant desired or nominal current value and supplies a constant torque. In this way, flank changes can reliably be prevented.
In one embodiment, auxiliary motors are coupled to measured value sensors and are operated under control with the aid of a feedback of the measured values. Here, too, both the angular position and the speed and also the acceleration can be measured. The measured value sensors required for this purpose are applied as close as possible to a separation location between the printing unit groups. Ideally, the measured value sensors are arranged on the paper-carrying cylinders immediately adjacent to a separation location. When predefining or prescribing a desired or nominal value for the controlled operation of the auxiliary motors, a differential angle in relation to the desired or nominal value used for the main motors is set, in order to avoid the occurrence of flank changes in the relevant partial gear train. As a result, an offset is achieved in the gear train of the respective printing unit group. The differential angle is set in such a way that the average auxiliary motor current always has a maximum negative value which, when a constant motor current is predefined or prescribed, just avoids flank changes.
Both when acted upon by a constant desired or nominal current value and during controlled operation of an auxiliary motor, interfering variable compensation can additionally be performed. The desired or nominal value for the main motors used under certain circumstances in a modified form for the auxiliary motors under controlled operation can be derived from a virtual line shaft or from a real value measured on a shaft of the printing press.
It is possible for a differential angle between a main motor and an auxiliary motor to be set variably so that the respective average actual current values of the auxiliary motors maintain a desired or nominal value. The sliding average of the auxiliary motor currents can be determined, for example, by filtering the auxiliary-motor desired or nominal current or actual current value.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a multi-motor drive and method for driving a printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.